Fluorescent whitening agents



FLUORESCENT WHITENING AGENTS Mario Francesco Sartori, Monroe Park, Del.,assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., acorporation of Delaware N Drawing. Application June 19, 1953, Serial No.362,945

9 Claims. (Cl. 260-3431) This invention relates to the production ofnovel organic compounds which are useful as whitening agents for fibrousmaterial such as textiles or paper. It is an object of this invention toproduce compounds of the above general nature, but which arecharacterized further by bleach fastness and by correct shade offluorescence. A further object is the production of whitening agents ofthe above class which are adapted for use on cellulosic fiber as well ason the hydrophobic fibers such as cellulose acetate, nylon,polyacrylonitrile fibers and polyethylene-terephthalate fibers.Additional objects and achievements of this invention will appear as thedescription proceeds.

The art of whitening or brightening textile fiber and paper is ofrelatively recent development. It has been found that fibrous materialswhich normally have a dull, yellowish cast when in the white, unbleachedstate, hecome whiter and brighter if treated with agents which fluoresceunder ultraviolet light. Presumably the action of the ultraviolet rayspresent in ordinary daylight is suflicient to excite these agents uponthe fiber to emit fluorescence which overcomes the undesirable tinge ofcolor in the unbleached fiber. Best results are obtained when the shadeof fluorescence is complementary to that of the unbleached fiber, sothat the colors will cancel out each other. Since the most commonoff-white shade of unbleached cellulosic fiber is yellowish, the mostdesirable shade in a fluorescent is blue.

Another very important demand developed by the trade is bleach fastness.Inasmuch as the aforementioned fluorescent agents are-generallyincorporated into soap and synthetic detergents, which are packaged andmarketed for household use, and inasmuch as in household practicelaundered articles are often subjected to bleaching with various agents,for instance hypochlorites, it is essential that the fluorescenttransferred from the detergent to the fiber shall not be destroyed bythe action of bleach. Unfortunately, most of the fluorescent agents nowon the market, and having the desirable blue shade, are weak in respectto this qualification of bleach resistance.

In addition to theabove two primary qualifications, a practicalwhitening agent should have good light-fastness, should be capable ofbeing synthesized economically from readily available materials, andshould have sufiicient fluorescent power (often referred to astinctorial strength) to give the desired effect at a minimum cost. Itmust also have afiinity for the fiber that is to be treated gndhshouldhave good exhaust qualities from an aqueous Now according to myinvention new chemical compounds are synthesized which have goodafiinity for cellulosic and hydrophobic fibers and produce thereon adesirable blue fluorescence, fast to light and to bleach. My novelcompounds may be designated generically as 3p-benzamidophenyhcoumarinswhich bear in the benzamido nucleus groups of substituents selected fromthe group of combinations consisting of one, two or three lower alkoxyradicals such as methoxy or ethoxy; one methoxy and one methyl radical;a methylene dioxy radical OC attached to two adjacent C- atoms.Accordingly, the novel family of compounds of this invention may beexpressed by the general formula 2,702,296 Patented Feb. 15, 1955wherein R is a phenyl radical bearing one, two or three lower alkoxyradicals, one methyl and one methoxy radical, or a methylene dioxyradical.

These compounds may be synthesized by several optional methods, forinstance:

A. By condensing 3-p-aminophenyl-coumarin with a benzoyl chloridebearing methoxy groups or other substituents from the above specifiedcombinations. The condensation is preferably carried out in pyridine orin hydrocarbon solvent containing a tertiary organic base, and thefurther details of procedure, including recovery may follow in generalthe teachings of Lubs et al., U. S. P. 2,497,130.

B. By condensing S-p-aminophenyl-coumarin with a benzoic acid havingmethoxy groups or other substituents of the groups above indicated. Thereaction mass in this case necessarily includes an acid halogenatingagent, such as phosphorus trichloride or oxyehloride, and the reactionis preferably carried out in pyridine or in a combination of ahydrocarbon solvent and a tertiary organic base, following in generalthe details of Lubs et al., U. S. P. 2,497,131.

The requisite 3-p-aminophenyl-coumarin employed as initial material forthe above synthesis may be prepared by reducing the corresponding3-nitro-compounds, and the latter in turn may be prepared by optional,known methods, for instance:

A. By coupling diazotized p-nitroaniline, with coumarin, in the presenceof cupric chloride. Further details on this process are given byMeerwein in Jour. fiir pragtische Chemie, vol. 152, p. 254 (1939).

B. By condensing salicylaldehyde with p-nitrophenylacetic acid,according to Walter, Jour. fiir prakt. Chemie, vol. 61, p. 186 (1900).

Without limiting this invention, the following examples are given toillustrate my preferred mode of operation. Parts mentioned are byweight.

Part I.Preparation of initial material B-(p-nitrophenyl) coumarin wasprepared from diazotized p-nitroaniline and coumarin, according to theaforementioned method of Meerwein (J. pr. Chem. 152, 254). The nitrogroup was then reduced as follows:

To a boiling suspension of 4.5 parts of 3-(p-nitro phenyl)coumarin inparts of ethyl alcohol, a solution of 22 parts of stannous chloride in30 parts of concentrated hydrochloric acid was added at the boil. Themixture was refluxed for 3 hours, then cooled and filtered. Theprecipitate was dissolved in water; the obtained solution was saturatedwith hydrogen sulfide and then filtered. The filtrate was made alkalinewith sodium carbonate. The obtained yellow precipitate was filtered offand crystallized from ethyl alcohol. Bright yellow crystals of3-p-aminophenyl-coumarin were obtained, melting at -182 C. and solublein ethyl alcohol with yellow fluorescence.

Part II.-Preparation of the whitening agents Example 1.-A suspension of1.1 parts of 3-p-aminophgnyl-coumarin, h0.9 part of m-methoxy benzoicacid an 0.7 part of p 0s h ous oxychlgride in 1 arts ofpyridintfivasmefi'fixe for mftwo room temperature, the mixture wasdrowned in water, made alkaline with 10% caustic and filtered. The crudeproduct was crystallized from ethyl alcohol. White crystals wereobtained, melting at 216 C. and soluble in ethyl alcohol with bluishfluorescence. This product is believed to be3-p-(3-methoxybenzamido)phenylcoumarin, of the formula Example 2.Asolution of 23.7 parts of 3-p-aminophenyl coumarin and 18.7 parts ofp-anisoyl chloride in 142 parts of pyridine was refluxed for one hour.After cooling to room temperature, the mixture was drowned in water andfiltered. The product was recrystallized from ethyl alcohol, yieldingwhite crystals, which melted at 231 C. and dissolved in ethyl alcoholwith bright bluish fluorescence. These crystals are believed to be3-p-(4-methoxybenzamido)-phenyl-coumarin.

Following the procedure of Example 1, but replacing the 0.9 part ofm-methoxy-benzoic acid by equivalent amounts of the acids indicatedbelow, the following additional compounds were synthesized:

Compound No.2

3. 3-p-(2-methoxybenzamido) phenyl coumarin (from o-methoxy-benzoicacid).

4. 3-p-(3-methyl 4 methoxybenzamido) phenylco%n)1arin (from 3-methyl 4methoxy-benzoic acr 5. 3-p-(2,4-dimethoxybenzamido) phenyl-coumarin(from 2,4-dimethoxy-benzoic acid).

6. 3-p-(3,4-dimethoxybenzamido)-phenyl coumarin (from3,4-dimethoxy-benzoic acid).

7. 3-p-(2,5-dimethoxybenzamido)-phenyl coumarin (from2,5-dimethoxy-benzoic acid).

8. 3-p-(2,4-diethoxybenzamido) phenyl coumarin (from2,4-diethoxy-benzoic acid).

9. 3-p-(2,4,5-trimethoxybenzamido) phenyl-coumarin (from2,4,5-tr'imethoxy-benzoic acid).

10. 3-p-piperonylamido-phenyl-coumarin (from 3,4-

methylenedioxy-benzoic acid):

COOH

The products of all the examples hereinabove exhibit the property offluorescence under ultraviolet light, and are suitable as whiteningagents for the purposes aforementioned. When applied to the hydrophobicfibers or cotton from a hot aqueous bath, preferably in the presence ofa soap or detergent, they impart to the fibers a bluishwhitefluorescence which is outstanding when viewed under ultraviolet light.

The products are also related to each otherin other physical properties,and their C, H and N analyses agreed well with those calculated fromtheir formulas.

Cotton and cellulose acetate fabrics were treated in aqueous bathscontaining commercial detergents (Tide, Surf) and various compounds fromthe above examples, and were then tested for afi'inity, tinctorialstrength (i. e., strength of the fluorescent effect produced upon astandard weight of the fabric by a standard weight of the compound beingtested), bleach fastness and light fastness (fadcometer exposure).Control samples of the same fabrics were tested simultaneously for eachcompound under similar conditions, except that no fluorescent agent wasadded to the aqueous detergent bath for treating the control. Finally,for the sake of exhaustive comparison, other samples of thecorresponding fabrics were treated with S-p-acetamido-phenylcoumarin, 3p benzamido phenyl coumarin (unsubstituted), and other known compoundsof the coumarin series.

The results showed that the unsubstituted benzamido phenyl coumarin hasvery poor afiinity for both cotton and hydrophobic fiber; the acetamidocompound is better in this respect, but has poor fastness to bleach;some of the other known coumarin derivatives (e. g.,7-diethylamino-4-methyl-coumarin) are fugitive to light; whereas thenovel compounds of this invention possess an admirable combination ofthese desirable practical properties, namely tinctorial strength, bleachfastness and light fastness.

The mentioned combination of desirable properties makes my novelcompounds excellently suitable for the whitening of textile fiber. Theymay, however, be used also for various other purposes where fluorescenceor absorption of ultraviolet light is desirable, for instance to achievefluorescent effects in costumes or stage settings, to achieve noveleffects on photographic paper, as ultraviolet filters when impregnatedon cellulosic films which are used for wrapping materials, etc.

wherein R is a phenyl radical carrying from one to three lower alkoxyradicals.

3. 3-p-(2,4-dimethoxy benzamido)-phenyl coumarin.

4. 3-p-(3,4-dimethoxy 'benzamido)-phenyl coumarin.

5. 3-p-(4-methoxy benzamido)-phenyl coumarin.

6. 3-p-(3-methoxy benzamido)-phenyl coumarin.

7. 3-p-(3-methyl-4-methoxy benzamido)-phenyl coumarm. 1

8. A process for preparing a fluorescent coumarin compound whichcomprises reacting in pyridine 3-paminophenyl coumarin with an aroylchloride of the formula RCOC1 wherein R is a phenyl nucleus hearingsubstituents selected from the following group of combinations: onelower alkoxy radical, two lower alkoxy radicals, three lower alkoxyradicals, one methoxy and one methyl radical, and a methylene dioxyradical attached to two adjacent C-atoms.

9. A process as in claim 8, the aroyl chloride being formed in situ fromthe corresponding carboxy acid and an acid halogenating agent.

Axelrad Feb. 8, 1944 Hoefle et al. Apr. 6, 1954 OTHER REFERENCES I.prakt. chem. 152, p. 241 (1939). Biochem. J. 45, p. 535 (1949).

1. A 3-P-BENZAMIDO-PHENYL-COUMARIN BEARING IN THE BENZAMIDO NUCLEUS AGROUP OF SUBSTITUENTS SELECTED FROM THE FOLLOWING GROUP OF COMBINATIONS:ONE LOWER ALKOXY RADICAL, TWO LOWER ALKOXY RADICALS, THREE LOWER ALKOXYRADICALS, ONE METHOXY AND ONE METHYL RADICAL, AND A METHYLENE DIOXYRADICAL ATTACHED TO TWO ADJACENT CATOMS.